1. Field of the Invention
The present invention relates to a novel polyimide, and more particularly to a novel, thermoplastic and amorphous polyimide, a preparation process thereof, and a novel aromatic diamino compound used for preparing said polyimide and a preparation process of the diamino compound.
The invention further relates to a polyimide-based resin composition comprising the polyimide and a fibrous reinforcement.
The aromatic diamino compound of the invention is useful as a raw material of polyimide of the invention and can also be applied to the raw material of polyamide, polyamideimide, bismaleimide and epoxy resin.
2. Related Art of the Invention
Polyimide is excellent in mechanical properties, chemical resistance, flame retardance and electrical properties in addition to its essentially excellent heat resistance, and thus conventionally has broad use in the field of forming materials, composite materials and electric- electronic appliances.
For example, a representative polyimide which has been known is Kapton and Vespel (Trade Mark of E. I. Du Pont de Nemours & Co.) which have recurring structural units of the formula (A): ##STR2##
The polyimide, however, is insoluble and infusible and thus must be formed by using a specific technique such as sinter molding by way of polyamic acid precursor. Such a difficulty results in problem in the processing step and it is thus difficult to obtain articles of a complex shape. Consequently, finishing operation such as cutting is additionally required in order to obtain satisfactory articles and causes a serious defect of high processing cost.
Another type of polyimide which has been known as amorphous and thermoplastic polyimide having an improved processability is Ultem (Trade Mark of General Electric Co.) which has recurring structural units of the formula (B). ##STR3## (U.S. Pat. Nos. 3,847,867 and 3,847,869)
The polyimide, however, has a glass transition temperature (hereinafter referred to as Tg) of 215.degree. C. and thus heat resistance is unsatisfactory.
The present inventors have found that polyimide having recurring structural units of the formula (C): ##STR4## is thermoplastic while maintaining heat resistance, solvent resistance and mechanical properties which are essential properties of polyimide (Japanese Laid-Open Patent SHO 62-205124, and HEI 1-110530 and 1-23830).
The polyimide, however, is essentially crystalline and causes crystallization by specific treatment.
Further, the present inventors have introduced recurring structural units obtained by using a compound of the formula (D): ##STR5## as a second diamine component into polyimide having recurring structural units of the above formula (C). As a result, polyimide of the formula (C) is made amorphous and a polyimide copolymer capable of being melt-processed at decreased temperature can be obtained (Japanese Patent Application HEI 01-90674). The polyimide copolymer, however, is also less-than-perfectly amorphous and has a defect of crystallization on standing for a long time at high temperature.
In order to solve such problem of polyimide, investigations have been tried to improve diamine components in the raw material.
For example, it has been tried to control glass transition temperature, melt flowability or crystallinity of polyimide by change of bonding radicals in monomer units, extension of polymer chain, or introduction of unsymmetrical structure, bent structure or bulky substituent.
Polyimide which is excellent in heat resistance and adhesion, has sufficient flowability in a molten state, and is outstanding in processability is still in the research-and-development stage.